Need help building backup

[electronist]

1N4148 is the diode number
Ceramic disk is right (0.1uF = 100 nF)
RL is a way of showing the Load (Load Resistance)
Ground means -ve of battery

Be careful of the Regulator. You will find the right circuit on the data sheet. Try studying and using the LM317 or LM117

Does your circuit have any upper voltage limit. I mean will it also work off 6V?

 

[engtech]

yes electronist...my device takes 2AA batteries=3volts...and thats all i know.

the second schematic you sent me...looks much better.

im going to buy the parts today and put this together,

hopefully i can let you know the results, im going to get a breadboard for this to make it much smaller.

THANKS!!!

if there is anything else you can let me know, please let me know. i seriously appreciate your work and time/effort helping me.

 

[engtech]

by the way...one end of the battery goes on the device and the other end of the solar cell goes on the device also?

 

[engtech]

**broken link removed**

thats what im working with, it just runs on two AA batteries.

 

[electronist]

What I would recommend is as follows:
First Connect only the Solar Cell and the regulator and check the output voltage across various the regulator by varying the light intensity. Do not connect the load as yet.
Search for the specifications of the sensor on Google.
I really doubt that your solar cell can provide enough curent to run the circuit shown. What is the current requirements of your load?

 

[Mr RB]

2 AA batteries is 3v, if you connect to the circuit like that through a 1N4148 diode you will get only 2.3v to the circuit. When the batteries are low (say 2.4 volts?) you will only get 1.7v to the circuit.

 

[engtech]

ok electronist, thanks for that info. I will buy the parts in the next 40 mins when my mom returns. should i add another battery to the device to make it work? or buy a rechargeable 4 volt hobby battery?

 

[engtech]

and i just wanna make sure that when the solar panel turns on, the battery power will shut down, main idea is to save battery power here and there.

THANKS.

 

[engtech]

Ok electronist, i've got the parts.

i also figured out that, i can't figure out how these parts will make it work so when the solar panel turns on, the batteries will turn off, the only other thing i can think of is have the batteries charge when the solar panel is lit, the only thing i will need for that to work is a device that can shut the power off from the solar cell once the batteries are fully charged. what can i add to that?

 

[summitville]

engtech, You never did specify what TYPE of rechargeable batteries you were using. You stated they are 1.5v each. That sounds more like Akaline Batteries - which are not rechargeble. Recharging a battery (properly) is not always a simple matter of just applying a fixed voltage.

But to satisfy your circuit requirements of ...

1) Run load/device from battery power when solar cell is dark
2) Run load/device from solar cell when sun is shining
3) Charge (NiCd/Lion/NiMh?) battery with excess solar power

You can you this "newnewcircuit" that I modified from Message #21.

You need to...
a) Pick a Type / Chemistry of rechargable battery.
b) Learn what max voltage that battery type needs to charge "properly" without also frying your load/device with too many volts.
c) Adjust the 1K variable resistor to provide that max voltage under full sunlight and fully charged battery.

The circuit max voltage is ~3.75V (load/device limit?) You can increase 1K to 2K if you need more volts from solar cell to "properly" recharge the battery but then you may over stress your load/device. If needed, you could add another LM317 after the battery to regulate output on load/device to 3.0 Volts.

OK ?

 

[engtech]

Hey Summitville, thanks for replying to my thread, i just wanna get somethin simple done here, i viewed your schematic.

basically i want to do one of the two,

1) the device currently runs on two AA batteries, i want to make it so when the solar panel switches on, i want the battery side to shut off.

or

2) have the batteries charge everytime they go low at a certain voltage point.

I've found a 6v rated solar panel from radio shack which i bought,

i've bought a lm317t voltage regulator,

i've bought diodes

i've bought radioshack brand rechargeable batteries (4 quantity)

Thats basically it right now.

i'm willing to buy whatever i need to make this work.

THANKS FOR ALL YOUR GUYS HELP SO FAR, IM GETTIN IDEAS, I'VE ALSO PLAYED WITH THESE DEVICES JUST A LITTLE BIT, BUT DUE TO FINAL EXAMS ITS TOUGH.

 

[summitville]

The circuit in mesg #21 can be used for Alkaline (regular / non-rechargable) batteries since there is no charging currrent. I think it needs some resistors added to the ADJ terminal (see app notes for LM317). Under Full Sun adjust the LM317 to output, after the diode and at the Device Terminals, for a voltage of ~3.0V. Also, that circuit adds a 0.7 Volt diode drop to the battery source. This voltage drop from 3.0V to 2.3V when running on only battery power may be critical to your Device / Load. You need to find out! The Solar Cell will drive the Device when the Solar Cell's Voltage is higher than the battery's voltage effectively turning the battery off. The two diodes make an OR circuit. Whichever Voltage Source, Solar Cell *OR* Battery, has the higher voltage will drive the Device and the other Source will be "turned off".

The Circuit in mesg #30 is for Rechargable Batteries only - not Alkaline/Regular batteries since there is charging current. This circuit runs as I explained previously. Are the rechargable batteries rated at 1.5 Volts? If not then will 2.4V (2 x 1.2 Volts) vs 3.0 V be an issue with your device?

 

[engtech]

thank you summitville, im running over to radioshack right now again, the solar panel is faulty. Get you guys the update tonite...appreciate it much.